Recently, the general trends in designing electronic devices are toward small size, light weightiness and easy portability. Moreover, with the increasing development of electronic industries, the internal circuitries of the electronic devices are gradually modularized. In other words, several electronic components are integrated into a single circuit module. For example, a power module is one of the widely-used circuit modules. An example of the power module includes a DC-to-DC converter, a DC-to-AC converter, an AC-to-DC converter, or the like. After the electronic components (e.g. capacitors, resistors, inductors, transformers, diodes and transistors) are integrated as a power module, the power module may be installed on a motherboard or a system circuit board.
Conventionally, the package structures of the power module are classified into three types. The first type of package structure is a single in-line package structure (SIP structure). After active components and passive components are mounted on a printed circuit board (PCB) or a substrate, a single row of leads are protruded from a side of the package structure by using a lead frame. The method of fabricating the single in-line package structure is easy by simply welding electronic components on the printed circuit board. Moreover, since the layout area of the single in-line package structure is large, the capability to withstand heat and the heat dissipating efficacy are both good. However, in addition to the active components, the traces of the printed circuit board or the substrate and safety distances between the electronic components may influence the overall area of the package structure. In other words, the area of the single in-line package structure is very large and occupies much space of the electronic device. Moreover, since all active components need to be previously packaged and the layout area is large, the overall fabricating cost is high. Moreover, since the single in-line package structure is manually installed on the system circuit board, the assembling process of the single in-line package structure is time-consuming and labor-intensive.
The second type of package structure is a land grid array (LGA) package structure. After the electronic components and the traces are installed on a printed circuit board, the electronic components and the traces are packaged by a molding process. In addition, plural contact pads are formed on a backside of the printed circuit board in order to be electrically connected with external device. In other words, the LGA package structure has a smaller layout area, a small overall volume and high density integration, and the method of fabricating the LGA package structure is simple and cost-effective. Moreover, the LGA package structure may be installed on a system circuit board by a surface mount technology. However, since the electronic components are arranged on the same layer of the printed circuit board, the traces between electronic components are still long. Under this circumstance, the line impedance is high, and a parasitic effect is easily generated. In other words, the electrical properties are possibly unsatisfied. Moreover, since the LGA package structure is only about to dissipate heat in a single direction, the heat dissipating efficiency is insufficient.
The third type of package structure is a ball grid array (BGA) package structure. Except that the signal output points of the BGA package structure are solder balls, the BGA package structure is similar to the LGA package structure. Since the BGA package structure has the solder balls, it is not necessary to print sold paste. That is, by simply printing flux, the BGA package structure may be installed on a system circuit board. In comparison with the LGA package structure, the BGA package structure is less prone to poor welding. However, since the process of forming the solder balls is complicated and expensive, the BGA package structure is not cost-effective. Moreover, the heat dissipating efficiency is still insufficient.
Therefore, there is a need of providing an improved package structure in order to eliminate the above drawbacks.